Wind turbines are well known as means of converting the kinetic energy of the wind into mechanical energy by the turning of rotor blades. In turn, the mechanical energy can then be converted into electrical energy by means of an electrical generator.
One type of a wind turbine used for electricity generation is comprised of a rotor with a multiplicity of long slender blades connected to a common spindle situated on the top of a suitably sized tower. An illustration of this type can be found in FIG. 1 of U.S. Pat. No. 8,622,698. Challenges faced in practice with this type of wind turbine are inefficiency at low wind speeds, the height of the towers and blades—required for safety and efficiency—and the overall intrusive appearance of such large structures. U.S. Pat. No. 8,622,698 also illustrates the common wind turbine tower used in practice: a slender, tall single element support.
In part, the efficiency of a wind turbine is predicted by Betz's Law. This law predicts that a wind turbine can only capture less than 16/27 (59.3%) of the kinetic energy of the wind. The limit arises as a result of the collision of air molecules that transfer their energy to the rotor blades.
In practice, wind turbines can only capture about 75 to 80% of the Betz's Law limit. However, a means of achieving higher efficiencies is to collect additional wind flow by the use of nozzles and diffusers before and after the rotor. The challenge is more fully described in US20120175882
Many wind turbines with shrouds or cowlings to create nozzles and diffusers are known in the art. One example is found at WO2012137008. Another is found at WO2006065248. An earlier type of wind turbine shroud specified for use on a tower structure is found at U.S. Pat. No. 4,075,500. However, in practice, the weight and wind load of the shrouds prove to be difficult to mount on wind turbine towers.
Other short-comings of wind turbines are found at paragraph 0014 and following of US2012282092. These include: inefficient operation close to the ground; large dimensions required by towers; expensive maintenance and cyclic stresses and failures.
One type of inefficiency in wind turbines is created by the wind currents which are created at the tips of blades. One means of solving this problem is to enclose the blades in a structure whereby there are no such currents. Such an arrangement is found in CA2590918 (at FIG. 3). In this patent, the drum also acts as a part of the electrical generator.
It would be beneficial if a wind turbine could be designed that would be efficient at lower wind speeds, could be installed without the use of the common wind turbine tower and could generally overcome the previously known short-comings of wind turbines in general. CA2590918 previously referred to teaches that a cowled turbine can be installed at the top of a wind turbine tower. CA25090918 also teaches the use of a fin to passively steer the turbine into the wind.
U.S. Pat. No. 4,140,433 teaches the elimination of the wind turbine mast. However, similar to CA2590918, U.S. Pat. No. 4,140,433 teaches only the use of a freely-rotatable turntable to ensure the turbine turns into the wind and the additional use of tail fins (Column 9, line 5) to ensure that the turbine self-centers in the wind.
Another short-coming of turbine design is the use of a single generator operating coaxially with or driven by the central shaft of the rotor of the turbine. Such a placement requires that the turbine be shut down for generator maintenance or repair. In addition, placement of the generator at the central shaft of the rotor generally involves difficult access in tight quarters. CA2590918 previously referred to, teaches the optional use of one generator driven by the circumference of the rotor (FIG. 5) but does not teach the use of a mechanical interruption or the use of more than one generator.
The use of only one generator in wind turbines limits their ability to efficiently generate electricity over a wide range of wind speeds. A generator sized for average expected wind speeds is generally inefficient at lower air speeds causing the wind turbine to be idled in such conditions.
A challenge with electricity generation is the losses of electricity in the transmission and distribution system. Significant amounts of electricity are lost in the simple transmission of electricity from one place to another. Because of this challenge, it is desirable that generation systems be placed close to where electricity will be used. The present invention allows generation capacity to be placed in close proximity to or, in suitable cases, on, buildings eliminating transmission losses.
A final challenge with systems related to electricity is the difficulty in storing excess electricity and smoothing out fluctuations in the electricity source. This challenge is pronounced when using wind to power electricity generators due to natural fluctuations in the wind. One means of solving this problem is by the use of flywheels and clutches as found in U.S. Pat. No. 8,749,083. However, the system proposed therein suffers the challenge of having to mount a heavy flywheel at the top of a wind turbine tower.
Liquids such as water may have flows similar to gasses such as air. A short-coming of the designs of most wind turbines is the inability to adapt those designs to areas of natural water flow in order to generate electricity.
Another shortcoming of most wind turbine designs is the lack of interoperability with other forms of motive force.